Small Craft Advisory 983, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
252 AM AKST TUE DEC 9 2014

.ANALYSIS AND UPPER LEVELS...
THE VERY BROAD UPPER LEVEL LOW CONTINUES TO BE CENTERED OVER THE
THE ALASKA PENINSULA WHERE IT WILL REMAIN ANCHORED THROUGH MIDWEEK.
AT THE MOMENT THE UPPER LOW STRETCHES OVER THE BERING...SOUTHWEST
ALASKA...EASTERN ALEUTIANS...MUCH OF THE GULF OF ALASKA AND INTO
SOUTHCENTRAL ALASKA BEING THE PRIMARY WEATHER MAKER FOR THE AREA.
THE LATEST OF NUMEROUS SURFACE LOWS ROTATING AROUND THE BIG UPPER
LOW IS CURRENTLY JUST TO THE SOUTH WEST OF KODIAK ISLAND. THIS LOW
WILL DRIFT SLOWLY WEST TO BE OVER THE ALASKA PENINSULA AS IT FILLS
IN OVER THE NEXT COUPLE OF DAYS. ADDITIONAL SMALLER TROUGHS
CONTINUE TO ROTATE AROUND THE LOW BUT WILL BECOME INCREASING
POORLY DEFINED AS THE LARGE VERTICALLY STACKED LOW WEAKENS AND
EVENTUALLY DISSIPATES.

ANOTHER WEATHER FEATURE OF NOTE IS THE SHORTWAVE TROUGH AND
ASSOCIATED SURFACE LOW WHICH TRACKS UP THE COAST OF SOUTHEAST
ALASKA TUESDAY AFTERNOON AND EVENING FOLLOWED BY A SECOND
STRONGER LOW WEDNESDAY AND THURSDAY. WHILE THESE LOWS WILL REMAIN
MOSTLY OUT OF THE AREA THEY WILL BOTH STRETCH INVERTED TROUGHS UP
ACROSS THE NORTHERN GULF AND INTO PRINCE WILLIAM SOUND.
ADDITIONALLY A SHORTWAVE TROUGH IN THE YUKON TERRITORY WILL TRACK
OVER THE COPPER RIVER BASIN AND INTO INTERIOR ALASKA TODAY.

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT IN THE SHORT TO MID TERM WITH MAIN
DIFFERENCES FOCUSED ALONG THE TIMING AND STRENGTH OF THE LOWS
ROLLING UP THE SOUTHEAST ALASKA COAST. THESE DIFFERENCES HOWEVER
WILL HAVE MINIMAL IMPACT ON EITHER FORECAST DOMAIN HERE. MODELS DO
DIVERGE A BIT MORE DETAIL WISE OUT IN THE LONG TERM HOWEVER ARE
ALL SUPPORTING THE ELEMENTS NECESSARY FOR A PATTERN SHIFT ALLOWING
MORE ACTIVE WESTERLY FLOW TO BEGIN BRINGING MORE AND STRONGER
FRONTAL SYSTEMS BACK INTO THE AREA NEXT WEEK.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE WEATHER FEATURES IMPACTING SOUTHCENTRAL ALASKA WILL CONTINUE
TO BE RATHER SUBTLE FOR THE NEXT COUPLE OF DAYS. CURRENTLY A
RATHER WEAK SHORTWAVE IS ROTATING THROUGH BRINGING SHOWERS TO MUCH
OF SOUTHCENTRAL ALASKA. IN MOST LOWER ELEVATIONS AREAS
TEMPERATURES ARE WARM ENOUGH FOR SHOWERS TO BE PREDOMINANTLY RAIN
ALTHOUGH ISOLATED PATCHES OF LIGHT FREEZING RAIN ARE POSSIBLE
AROUND THE ANCHORAGE AREA OVERNIGHT. THIS COULD BECOME MORE OF A
WIDESPREAD CONCERN IF THE COMBINATION OF DIMINISHING WINDS AND ANY
BREAKS IN THE CLOUDS ALLOW FOR MORE RAPID RADIATIONAL
COOLING...BUT FOR NOW ANY FREEZING RAIN LOOKS TO REMAIN RATHER
ISOLATED AT BEST.

ANOTHER FEATURE TO WATCH IN THE NEAR TERM IS AN UPPER LEVEL
DISTURBANCE TRACKING FROM THE YUKON TERRITORY OVER THE COPPER
RIVER BASIN EARLY THIS MORNING. AS THIS WAVE SPREADS IN FROM THE
EAST IT WILL BRING A GOOD POTENTIAL OF SNOW SHOWERS WITH IT
ESPECIALLY TO THE WRANGELL MOUNTAINS AND THE EAST SLOPES OF THE
TALKEETNA MOUNTAINS.

AS WE MOVE INTO TONIGHT AND WEDNESDAY IT IS NECESSARY TO LOOK
FURTHER AWAY TO FIND THE WEATHER SYSTEMS DRIVING THE WEATHER OVER
SOUTHCENTRAL ALASKA. ONE OF THESE SYSTEM IS THE STRONG LOW THAT
TRACKS FROM THE NORTHEAST PACIFIC AND THEN UP THE SE AK PANHANDLE
COAST TUESDAY EVENING. THIS SURFACE LOW WEAKENS OUT TO BROAD
SHALLOW TROUGH PRETTY QUICKLY TONIGHT BUT THAT DIFFUSE FEATURE
WILL EXTEND NORTH AND WEST OVER THE NORTHERN GULF AND TOWARDS
PRINCE WILLIAM SOUND FLATTENING PRESSURE GRADIENTS SIGNIFICANTLY
ALONG THE NORTHERN GULF COAST AND INTO PORTIONS OF SOUTHCENTRAL
ALASKA.

TO SOME EXTENT...REMNANTS OF THIS WEAK TROUGH WILL ALSO PHASE
WITH A SOMEWHAT STRONGER SHORTWAVE ASSOCIATED WITH THE ALASKA
PENINSULA LOW LIFTING NORTH OVER THE KENAI PENINSULA LATE TONIGHT THROUGH
WEDNESDAY MORNING. THE COMBINATION OF THE LIFT FROM THE SHORTWAVE
AND THE SLACKENING SURFACE PRESSURE GRADIENT ENDING ANY DOWN
SLOPING EFFECTS WILL BRING THE POTENTIAL FOR SOME LIGHT SNOW TO
THE AREA.

A STRONGER BUT OTHERWISE FAIRLY SIMILAR SURFACE LOW WILL FOLLOW
THE SAME TRACK TO BE WEST OF HAIDA GWAII WEDNESDAY EVENING THEN
CONTINUE NORTH TO BE JUST WEST OF SITKA THURSDAY NIGHT. THIS LOW
WILL EXTEND A SOMEWHAT MORE ORGANIZED AND A LITTLE DEEPER INVERTED
TROUGH ACROSS THE NORTHERN GULF AND TO PRINCE WILLIAM SOUND
WEDNESDAY NIGHT AND THURSDAY. MEANWHILE THE REMAINS OF THE ALASKA
PENINSULA LOW WILL DRIFT EAST TO KODIAK ISLAND DURING THIS TIME
PERIOD SUCH THAT THE INVERTED TROUGH EXTENDS SOUTHWEST STRETCH
ACROSS MUCH OF THE GULF COAST WITH A BROAD AREA OF WEAK FLOW OVER
THE KENAI PENINSULA...KODIAK ISLAND AND OTHER COASTAL AREAS OF
SOUTHCENTRAL ALASKA.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SHOWERS FROM THE WAVES ROTATING AROUND THE LOW CENTERED SOUTH OF
THE ALASKA PENINSULA CONTINUE TO MAIN IMPACT ON SOUTHWEST ALASKA.
CURRENTLY THE NEXT BAND IS CROSSING THE ALASKA/ALEUTIAN RANGES AND
HEADING EAST OVER THE BRISTOL BAY AREA. PRECIPITATION TYPE
QUESTIONS WITH THIS WAVE AND SUBSEQUENT ONES FOR THE NEXT SEVERAL
DAYS REMAIN THE MAIN FORECAST CHALLENGE WITH BRISTOL BAY THE MOST
COMPLEX ZONE. IN AREAS CLOSER TO THE MOUNTAINS WHERE DOWNSLOPE
WARMING CONTINUES SHOWERS WILL REMAIN RAIN. FURTHER TO THE WEST
NORTH TO NORTHEAST WINDS CONTINUE TO RECHARGE LOW LEVEL COLD
AIR...FREEZING RAIN AND SLEET ARE A CONCERN BEFORE SHOWERS TURN
OVER TO ALL SNOW AND QUICKLY TAPER OFF FURTHER TO THE NORTH.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
MINIMAL CHANGES EXPECTED WITH NORTHERLY FLOW AND SMALL EMBEDDED
SHORTWAVE TROUGHS CONTINUING TO PRODUCE NUMEROUS BANDS OF SHOWERS
THROUGH WEDNESDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE LARGE AND STAGNANT UPPER LEVEL TROUGH PATTERN WILL FINALLY
BEGIN TO BREAK DOWN WEDNESDAY AND THURSDAY AS TWO SURFACE LOWS
RAPIDLY DEEPEN ALONG THE STRONG JET STREAM WELL TO THE SOUTH. THE
FIRST IS A SYSTEM IN THE EASTERN PACIFIC WHICH WILL RAPIDLY DEEPEN
AS IT SWINGS TOWARDS THE BRITISH COLUMBIA COAST TUESDAY NIGHT AND
WEDNESDAY. WHILE THIS SYSTEM WILL HAVE LITTLE DIRECT IMPACT ON
THIS FORECAST AREA IT WILL SUCK A GOOD BIT OF THE REMAINING ENERGY
OUT OF THE LARGE UPPER LOW AND BEGIN TUGGING IT TO THE EAST.

THE SECOND LOW...FAR OUT IN THE PACIFIC DEEPENS INTO THE 960S
WEDNESDAY IN THE VICINITY OF 40N 170E THEN CONTINUES QUICKLY TO
THE EAST-NORTHEAST. WHILE MOST OF THE ENERGY OF THIS IMPRESSIVE
STORM WILL STAY WELL TO THE SOUTH THE BIGGER IMPACT FOR THIS AREA
WILL BE THE UPPER LEVEL RIDGE THAT IT PUMPS UP OUT AHEAD OF
ITSELF. IT IS THIS AMPLIFIED RIDGE THAT WILL FINALLY WEAKEN AND
REMOVE THE OLD UPPER LOW AS IT SLIDES EAST ALONG THE ALEUTIAN
ISLAND THURSDAY AND OVER THE ALASKA PENINSULA THURSDAY NIGHT. THE
SURFACE LOW WILL REACH THE CENTRAL GULF AROUND SATURDAY AND WHILE
IT WILL HAVE BEEN WEAKENING FOR A WHILE AT THIS POINT IT WILL HAVE
OPENED THE DOOR FOR A MORE ACTIVE FLOW PATTERN AND ADDITIONAL
PROGRESSIVELY STRONGER SYSTEMS TO THE START MOVING IN FROM THE
WEST NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 177 178 185.
         HEAVY FREEZING SPRAY 181.
FIRE WEATHER...NONE.

&&

JER